In the diagram, BD = 9, CE = 7, [ABC] = 30, and [ADE] = 20. Find [ACD]
https://latex.artofproblemsolving.com/4/4/a/44a0385ed03d62054a89d5f89dbfe8d93195d0b5.png
All triangles share the altitude.
Let CD be X. Let the shared altitude be Y.
Make some equations!
(1/2) * y(9-x) = 30
(1/2) * y(7-x) = 20
I think from here you pretty much solve for X and Y.
Once you have those values, you can do (1/2) * X * Y for the answer.
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